Midbeam instead of lintel

[kalaiyarasanbim]

Hi,

 Refer the image.

   Now I am following  image 01.

       1. But i want follow Image 02 to reduce the concrete and steel.

       2.If i choose image 03, as per my project lintel are designed to carry 4m blockwork.

          so that location can i ignore the midbeam?

   I need technical explanation for this issue which one is better?

Thanks

kalai

[RDAOU]

@kalaiyarasanbim 

All three options work; however; 

1. Image 1...the lintel is overdesigned. You shouldn't need 40cm (this option offers more flexibility when later setting out the doors or in the event of any future change or modification which might effect the door height.
2. Image 2...you saved yourself a lintel but
   • you will have 0 tolerance in case of future modification or rectification where chipping might be required.
   • this might generate more cost in terms of blockwork and plastered finishes (the joint will between block and concrete will need to be reinforced to prevent cracks - hence, preferable that the mid-beam is set out above false ceiling level
   • The mid, beam is ideally set out at an elevation where the last row below beam is a standard size size (full or half block). That rarely to never works when aligning beam with door height
3. Image 3 … more or less similar to Image 2

Ideally, work with Image one and size the lintel properly

[MostafaElashmawy]

From my point of view option 1 is the best but with some adjustments.

I would go for precast smaller lintel that can be added later. in that case, you will cast the columns and beams with one connection only. that's more practical for site. 

1- cast columns to the bottom of  main beam.

2-cast the main horizontal beam.

3- continue with the columns.

4- add the precast beams supported on steel angels for example which will be anchored to the columns.

check below photo.

another option would be to move the columns away from the door in your design then do same steps 1 to 3. and then add the lintel directly on the block right and left of the doors. 

check below photo

sometimes being very economic would not be practical for site . but technically all your options are ok.

[ToanDN]

- I am not a structural engineer but if you want to offset the floor beams then you need to recalculate the lateral force to the columns and possible need to upsize them. There you are not saving concrete and steel already.
- If you have a floor at the main beam level then you would want to have a beam as shown in image 1 to support the floor edge there.
- There are only a few rows of bricks above the door and below the main beam so the lintel should be much smaller.

In general, you need to look at the bigger picture to understand primary and secondary structure and place the priorities where they should be.

[kalaiyarasanbim]

Thanks.

And what will happen if i choose image 3 ? 

(in this case we have tolerance also. 

lintel design wise safe to carry that much block work.)

[RDAOU]

@kalaiyarasanbim 

Technically speaking it is preferably work with option 1 and resize the Lintel (h=20 is more than sufficient) which can be pre-casted and fixed on steel angles as @MostafaElashmawy suggested, or it can even be steel lintel in this case … Execution wise this is faster considering that the concrete (columns/beams) is casted 1 step less and overall, this option saves you more on both the time and cost. 

Width wise, it is better to fix subframes on concrete than on blockwork, so you should be fine  if you consider for "Door structural width + Xcm" depending on whether such doors have a necked or flush frames / with or without subframes